A new Army report confirms it was a mid-air crash that brought down two Army helicopters at Washington’s Joint Base Lewis-McChord a year ago. It happened during a night vision training exercise.

The heavily redacted 190-page report aims to recreate the events of the night of December 12, 2011. That clear, moonlit evening two Kiowa Warrior helicopters took off within a minute of each other. On board each chopper was an experienced pilot instructor and a newer pilot in training.

According to the report, at about 7:42 p.m. the first chopper crossed a training area and smashed into the rear of the second helicopter. The impact sent the helicopters spinning into the ground. They came to rest in a heavily wooded area. One of the choppers caught fire.

All four pilots, three men and one woman, were killed. Crash scene photos show mangled metal that’s hardly recognizable as an aircraft. Investigators did make seven findings and recommendations, but the Army redacted them in the public report.

A previous investigation found base commanders were aware of radar and radio limitations in the training area where the crash happened.